The present invention relates to a magnetic fluid shaft-sealing device and, more particularly, to a magnetic fluid shaft-sealing device for a pump.
It is well known to mount a mechanical seal or a magnetic fluid seal in a pump for sealing between a pump housing of the pump and a rotary shaft in the pump housing. A typical magnetic fluid seal device generally includes a plurality of annular magnets mounted in an interior of the pump housing and around the rotary shaft or a shaft sleeve. Each magnet is sandwiched between two pole pieces also mounted around the rotary shaft. A magnetic liquid is filled in a sealing gap between an outer periphery of the rotary shaft and inner peripheries of the pole pieces. The rotary shaft and the poles pieces are made of magnetizable material. A closed magnetic circuit with magnetic force is created by flows of magnetic field lines from the magnets through the poles pieces, the rotary shaft, and the magnetic liquid and, thus, retains the magnetic liquid in the sealing gap to provide a sealing effect between the pump housing and the rotary shaft. The sealing effect of the magnetic fluid seal device mainly depends on the ability of keeping the magnetic liquid in the sealing gap. In such a magnetic fluid seal device, the magnetic liquid in the sealing gap tends to escape from openings in two sides of the sealing gap due to centrifugal force generated during rotation of the rotary shaft. To avoid this problem, it is generally necessary to increase the number of the magnets and/or decrease a width of the sealing gap in a radial direction. However, it is inconvenient to manufacture and assemble the magnetic fluid seal device in a narrow sealing gap. Further, more magnets lead to bulky structure and increased costs.
Thus, a need exists for a magnetic fluid seal device that can securely retain the magnetic liquid in the sealing gap while allowing easy assembly.